ThunderDome is a system for collaboratively measuring upload bandwidths in
ad-hoc peer-to-peer systems. It works by scheduling bandwidth probes between
pairs of hosts, wherein each pairwise exchange reveals the upload constraint of
one participant. Using the abstraction of bandwidth tournaments, unresolved hosts
are successively paired with each other until every peer knows its upload
bandwidth. To recover from measurement errors that corrupt its tournament
schedule, ThunderDome aggregates multiple probe results for each host, avoiding
pathological bandwidth estimations that would otherwise occur in systems with
heterogeneous bandwidth distributions. For scalability, the coordination of
probes is distributed across the hosts. Simulations on empirical and analytic
bandwidth distributions---validated with wide-area PlanetLab experiments---show that
ThunderDome efficiently yields upload bandwidth estimates that are robust to
measurement error.